graves that are not clearly visible: Or “unmarked graves.” In general, Jewish tombs do not appear to have been ornate or ostentatious. As shown in this verse, some were so inconspicuous that people might have walked on them and become ceremonially unclean without being aware of it. The Law of Moses considered unclean those who had touched anything belonging to the dead, so a person walking on such unseen graves would become ceremonially unclean for seven days. (Nu 19:16) So that graves could be easily discovered and avoided, the Jews had them whitewashed each year. In this context, Jesus evidently meant that people who mixed freely with Pharisees, believing them to be good men, subconsciously became infected with their corrupt attitudes and unclean thinking.​—See study note on Mt 23:27.